fix: Add validation for interest groups and fix execom roster leaks

[DevWithPranav]

No description provided.

[greptile-apps]

Greptile Summary

This PR replaces title-based execom detection with explicit role classification and adds interest-group validation. The main changes are:

• Adds is_execom_role to the role model and IG role creation paths.
• Filters campus execom rosters using the new role flag.
• Prevents non-execom role titles from being reused for execom roles.
• Limits user profile edits to three interest groups.

Confidence Score: 2/5

The role schema and existing-role classification can break the campus execom workflow and need fixes before merging.

• The unmanaged model field has no matching database schema artifact.
• Existing execom roles retain the false default and disappear from roster results.
• New IG role creation paths consistently set the intended classification.

db/user.py and api/dashboard/campus/events_views.py

Important Files Changed

Filename	Overview
db/user.py	Adds an unmanaged Role field without the required physical schema change.
api/dashboard/campus/events_views.py	Uses the new execom flag for roster filtering and role assignment without backfilling existing roles.
api/dashboard/campus/dash_campus_helper.py	Classifies newly created or updated IG campus-lead roles as execom roles.
api/dashboard/ig/dash_ig_view.py	Adds execom classification to roles created with an interest group.
api/dashboard/user/dash_user_serializer.py	Limits the submitted interest-group list to three entries.

_{Reviews (1): Last reviewed commit: "Merge pull request #3059 from gtech-mule..." | Re-trigger Greptile}

[greptile-apps]

Role Column Missing From Schema

Role is unmanaged, but no matching schema.sql or alter-scripts/ change adds this column. Deployments using the repository schema will make ORM reads and the new execom filter reference a missing column, causing role-backed API requests to fail with a database error.

[greptile-apps]

Legacy Execom Roles Stay Unclassified

The new column defaults to false, and this PR does not backfill existing custom execom or IG campus-lead roles. Once the column exists, members holding those roles disappear from the roster even though the old blacklist included them; the assignment path also rejects their existing role titles as non-execom.